User Manual - pancroma

29. AJISANE Algorithm________________________________________________________________PANCROMA TM contains an implementation of the AJISANE transform. Thisalgorithm is similar in some ways to the HSI algorithm. It is capable oftransforming any number of spectral channels into an orthogonal color spacequalified by an intensity vector. As a result, it is possible to transform the blue,green, red, and near infrared (NIR) bands into the AJISANE space, substitute thepanchromatic band for the intensity band, and then reverse transform back toRGB space.The advantage of such a four-dimensional transform is that some panchromaticbands (notably Landsat) overlap into the NIR band. As a result, substitution ofthe panchromatic band for the intensity band in the HSI algorithm can result inspectral distortions, as described previously. Because the AJISANE space cancontain NIR information as well as RGB information, this type of spectraldistortion can be reduced. AJISANE is more memory expensive than XIONG,the other PANCROMA TM five-file pan sharpening method. However, it can offeran alternative for those cases where the use of XIONG results in unwantedartifacts as described in a previous article.To use the AJISANE transform, open five band files by selecting ‘File’ | ‘Open’,opening the blue, green, red, panchromatic, and near infrared bands in this exactorder. As always, the band files must all be of exactly the same dimensions andthe panchromatic band must be a 2X, 3X, 4X or 6X multiple of the band file sizes.When the files are open, select ‘Pan Sharpening’ | ‘AJISANE Transform’. Youcan select either the ‘Simple’ or the ‘Enhanced’ computation methods. The twodiffer in how they compute the adjusted intensity array from the panchromaticarray. The Enhanced computation takes a bit longer but may offer better colorfidelity in some files than the Simple computation. The trade off is a slight loss ofpan sharpened image resolution.After choosing the computation method, the Pan Sharpening Input box willbecome visible. You must input the number of interpolation iterations using thedrop-down combo box. PANCROMA TM will automatically select Laplacianinterpolation for any panchromatic file size greater than 2X and will assign adefault interpolation factor of 10.If you wish to assign more Laplacian iterations, if you wish to add Thin Plateiterations or if you wish to conduct an Iterative interpolation, you must check the‘Activate Image Processing Routines’ check box on the Main Window. When youdo so, you can check the ‘Thin Plate Check Box’ and assign Thin Plate iterations.You will also have the option of checking the ‘Landsat Color Enhancement’ checkbox. Checking this box invokes special image processing algorithms to help75